1. Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China, Fax: +86‐21‐64166128
2. Hunan University of Chinese Medicine, Changsha, Hunan Province 410208, China
3. Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire, RG42 6EY, UK